Infrasonic intrusion detection system

ABSTRACT

The disclosed system detects any change in the net crosssectional opening area between the inside and outside of an enclosed contiguous volumn. A slowly varying small cyclic pressure variation is generated within the protected volume by a small motor driving an oscillating piston or baffle located in a perimeter wall. As the piston moves back and forth air is moved through the existing leakage paths resulting in a fixed average power level required of the driving motor. Any change in the cross-sectional opening area or air leakage path will result in a change in the average power required to move the piston and this change in power level may be used to activate an alarm means.

United States Patent [191 Haselton [451 Dec. 10, 1974 INFRASONIC INTRUSION DETECTION SYSTEM [22] Filed: July 19, 1973 [21] Appl. No.: 380,798

Primary ExaminerDavid L. Trafton Attorney, Agent, or FirmPollock, Philpitt & Vande Sande [57] ABSTRACT The disclosed system detects any change in the net cross-sectional opening area between the inside and outside of an enclosed contiguous volumn. A slowly varying small cyclic pressure variation is generated within the protected volume by a small motor driving an oscillating piston or baffle located in a perimeter wall. As the piston moves back and forth air is moved through the existing leakage paths resulting in a fixed average power level required of the driving motor. Any change in the cross-sectional opening area or air leakage path will result in a change in the average power required to move the piston and this change in power level may be used to activate an alarm means.

10 Claims, 2 Drawing Figures PATENTELEEBIOW 3854.129-

FIG. l.

BACKGROUND OF THE INVENTION While a great number of intrusion detectors and alarm system have been developed for bank vaults and other relatively small confined areas, few systems have been developed which will adequately protect a residential home. Those systems which have been designed to protect homes are either inadequate, or extraordinarily expensive. Due to the large number of openings, that is windows and doors, which are found in the average dwelling, it becomes prohibitively expensive to protect' each of the openings with a conventional burglar alarm system. Furthermore, those systems are normally installed after the home has been constructed, and a complete burglar alarm system would involve extensive rewiring of the home, or unsightly wires arranged around the interior of the home. Furthermore, most of these systems are easily surmounted by the skilled burglar.

Capacitance, light beam. ultrasonic, and floor pressure activated alarm systems have been used quite successfully for special applications wherein a smallarea is protected or a specific location is protected. These types of systems are unsuitable for dwellings since pets and small children may move about in the evening after the alarm has been activated.

Constant pressure generating systems have also been used with some success for bank vaults and other relatively-confined volumes wherein the leakage rate is quitelow and the area to be protected is small. This type of system is notgenerally transferrable to the average dwelling because of the large amount of leakage involved in the dwelling as well as the wind effects thereon. If the dwelling is constantly pressurized or underpressurized to any significant degree, the heat loss through chimney flues, plumbing vents and even construction irregularities becomes extremely significant.

PRIOR ART The prior art discloses burglar alarm systems which utilize ultrasonic acoustic waves to protect an enclosed volume. As pointed out previously, this type of alarm system is generally unsatisfactory for the average dwelling since the normal nocturnal movement of the dwellings inhabitants is sufficient to activate the alarm system. In addition, these systems are generally sized to protect only a relatively small area per system.

The prior art also discloses enclosure protecting devices that use a constant over-pressure or underpressure technique for the area to be protected. In these devices a change in the pressure caused by the unauthorized opening by a door or window is used to activate the alarm. As indicated above, this type of alarm system is not satisfactory for the average dwelling since the over-pressurization required to make the alarm system work would cause a great deal of heat loss through chimney flues, bathroom vents and leaks around doors and windows. If the home contains a fireplace, the loss would be substantially greater. The combined total of the openings through which losses occur necessary to make the device function, would make the cost of operating the system prohibitive. Additionally, wind loading becomes an important factor in the operation of this type of systemsince a change in wind direction or gusting of the wind can result in the activation of the alarm.

OBJECT OF THE INVENTION It is therefore an object of the present invention to provide a simple and inexpensive intrusion detector system for dwellings and homes. It is a further object of the present invention to provide an alarm system which will utilize alternating over-and under-pressurization to avoid the heat loss or gain which would normally be encountered in a residential dwelling.

The object of the present invention is to detect any increase in the net cross-sectional area of the openings which connect the inside and outside of a dwelling. If one of the windows is broken or opened by an intruder, the cross-sectional opening area connecting the inside and outside of the dwelling is substantially increased. If a door is opened, the cross-sectional area is substantially increased. If a wall is broken through, the area is substantially increased. I

The present invention generates infrasonic alternating pressure variations within the volume or dwelling which results in over-pressurization and subsequent under pressurization during each cycle. The means used to generate the over-pressurization and under-pressurization comprises a baffle .which is mounted in the dwelling wall. The motor used to drive the baffle is mounted on a reaction bar which is resiliently mounted to the dwelling structure. The force used to reciprocate the baffle is transmitted via the motor to the reaction bar and the bar itself moves with respect to the dwelling in a manner which is proportional to the force required to reciprocate the baffle. Any increase in the cross-sectional opening will result in a substantial change in the average required power to move the baffle, and the net change in power is used to activate an alarm which indicates that a door or window has been opened.

It is a further object of the invention to provide means for compensating for ambient windloading or gusting. Since the detection means of the present invention measures the average power required to reciprocate the baffle, a steady windloading will alternately aid and resist the baffle motion in equal amounts resulting in a zero net power change over a complete cycle or series of cycles. This avoids the activation of an alarm due to ambient windloading. An averaging means is used to prevent activation of the alarm due to a gusting wind. A gusting wind will normally be neutralized in the manner noted above so that the net power required is zero during most situations. In the unlikely event that the wind gusts occur at the same frequency and in phase with the baffle movement in such a manner as to ease the driving power requirement a false alarm could be initiated. By averaging the net power increase or decrease over a period of time, the statistical probability of gusting occurring precisely in a constant phase relationship with the baffle over a period of cycles becomes almost insignificant.

DESCRIPTION OF THE DRAWING FIG. 1 is an electrical schematic of the circuit used to activate the proposed alarm.

FIG. 2 is a cross-sectional view of the baffling means used to produce the pressure waves of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention includes means for generating alternating pressure variations within a confined space. Although the prior art has used a fan or other steady pressure differential devices to activate leakage rate alarms, the present invention contemplates a movable baffle positioned in the exterior wall of an enclosed space. For a normal dwelling house, it is preferable to mount the baffle in the ceiling or window of the top floor, which places the baffle in communication with the interior atmosphere of the dwelling on one side, and exterior ambient air on the other side.

FIG. 2 illustrates in diagrammatic and cross-sectional form one means for producing alternating pressure variations within a confined space.

The confined space is enclosed by a perimeter wall which is represented in cross-sectional form as ceiling 11 in FIG. 2. A reciprocating baffle 12 is mounted for reciprocation on guide arm 14 within cylindrical support means 13. An electric motor 15 is used to drive the reciprocating baffle through a crank arm 16 and a connecting rod l7.'The electric motor 15 is mounted on a reaction bar 18 which is secured to the dwelling structure by means of springs 19 and and cylinder means 13. Thus, the force used to drive baffle means 12 is transmitted by the crank arm 16 and connecting rod 17 to the motor means 15, and from the motor means 15 to the reaction bar 18 which is restrained in its motion by springs 19 and 20. The alternating tension and compression of springs 19 and 20 is representative of the average force used to drive baffle 12 along its reciprocating path.

The reaction bar 18 has mounted thereon a flexible contact arm 21 which is normally restrained by a dashpot 22 affixed to the dwelling structure by means of bracket 23. Bracket 23 also supports a fixed contact 24 adjacent the flexible contact 21. The function of the dashpot and flexible contact arm will be hereinafter later described.

While a reciprocating baffle has been illustrated in FIG. 2, it should be understood that a pivoted baffle or a bellows unit could be substituted for the baffle means as an alternate embodiment. It is essential that the device be able to generate alternating pressure variations within the dwelling. and that the reaction force required to generate the variations be measurable.

. Baffle means 12 reciprocates at a relatively low infrasonic frequency. This reciprocation may be at any frequency under 10 cycles per second. As the baffle member 12 reciprocates back and forth, it sets up an alternating pressure differential or variation throughout the dwelling with respect to the outside air..ifa steady pressure source were used, the air would be quickly exhausted through fireplace flues, furnace flues, plumbing vents, and leakage around windows and doors. In the present invention however, a slug" of air will be formed in the relatively long flue paths, the fireplace, furnace, and vent pipes, and this slug of air will reciprocate upwardly and downwardly along the flue path as baffle member 12 reciprocates along guide arm 14.

' Thus, the slug" of air prevents any substantial heat loss from the dwelling caused by over-pressurization or under-pressurization. Since the bulk of the crosssectional area is found within the relatively long flow paths defined by the fireplace and furnace flues, the net result is a greatly diminished loss ofinternal ambient air to the exterior of the dwelling. The leakage around doors and windows is a relatively minor fraction of the total cross-sectional area through flues and vent pipes.

The motor housing of drive means 15 is attached to reaction arm 18 and is free to rotate about an axis common to that of crank arm 16 within the constraints imposed by the springs 19 and 20.

The power delivered by drive means 15 to the baffle 12 results in a counteractive force acting on reaction bar 18 which causes it to be rotated against the restraining forces of springs 19 and 20 in a direction counter to the motion of crank arm 16. Thus, the deflection of reaction arm 18 will be proportional to the instantaneous power being exerted by drive means 15 against baffle l2, and will vary during each cycle of baffle 12 depending on the instantaneous velocity of baffle 12, the air leakage paths which exist through the dwelling, and the existing windloading. The average deflection of the reaction arm 18 is therefore directly related to the average power exerted by the drive means 15 during one complete baffle excursion. Because of wind effects, it is desirable to average the excursions of reaction bar 18 over one or more complete cycles of baffle 12. This averaging is accomplished by means of a mechanical filter element comprising the resilient contact 21, and dashpot 22. Under normal operation, springs 19 and 20, and the average position of reaction bar 18, maintains a slight gap between the flexible contact 21 and fixed contact 24. This maintains an open electrical circuit between circuit lines 25 and 26.

In the event a window or door in the perimeter wall 11 is opened by an intruder, the increased air leakage path will result in a reduced resistance to motion for baffle 12. This will thereby reduce the reactive force generated between baffle l2 and drive means 15, and a reduction in the average torque exerted on reaction bar 18 such that the springs 19 and 20 will tend to rotate the reaction beam 18 to a normal position in a direction opposite the force normally exerted by drive means 15. As the average angular rotation of reaction beam 18 rotates clockwise as illustrated in FIG. 2, the averaging function of resilient contact 21 and dashpot 22 will allow contacts 21 and 24 to close thus energizing the alarm system illustrated in FIG. 1.

If desired, an additional contact similar to that of 24 could be installed in the opposite side of resilient contact 21 to sense any decrease in the average leakage area.

When contacts 21 and 24 are closed, the circuit lines 25 and 26 are closed and energizes the alarm system illustrated in FIG. 1. This alarm system includes an off and on switch 27 for disengaging the alarm when not in use. The system also includes a battery or other electrical source 28 for energizing the alarm, and a relay means 29. It is desirable that relay means 29 be of the self-latching type so that once contact is made between the resilient contact arm 21 and the fixed contact 24, the alarm system 30 will be continuously activated until reset manually, or reset by a timing device. The closure of contacts 21 and 24 results in the closing of relay 29, and the activation of alarm 30. Although a DC. power source and DC. relay and alarm have been illustrated in FIG. 1, it is to be understood that alternating-current components could be used and the entire system activated from the house current. Alarm means 30 may take the form of any conventional alarm such as a bell, horn, siren, flashing light, or combination thereof.

In summary, when the alarm system is activated by closing switch 27 and activating motor 15, the motor will drive baffle means 12 back and forth along its reciprocal path within which cylinderical means 13 will experience compressive resistance to the air contained within the structure dwelling. There will of course be some energy loss in the frictional contact accompanying the slight air motion within the structure, but the frictional losses are insignificant. The compressive resistance will be a direct function of the air leakage rate between the internal ambient air and the external ambient air on the other side of ceiling 11. This compressive resistance will of course be larger for small leakages and smaller for large leakages. As the baffle reciprocates back and forth, the average reactive forces are transmitted through the crank linkages 16 and 17 to motor and from motor 15 to reaction bar 18. This reactive force is then translated by bar 18 into rotary motion opposite that of crank arm 16. In the embodiment illustrated in FIG. 2, the crank arm 16 rotates clockwise, while the reaction beam tends to rotate counterclockwise. Spring tension exerted by springs 19 and 20 in reaction to the torque of reaction bar 18, and the averaging effect of dashpot 22 normally restrain resilient contact 21 from contacting the fixed bar contact 24. However, when the average rotation of reaction bar 18 exceeds a predetermined amount due to reduced torque, contact is made between contact arm 21 and fixed contact 24. This results in the closing of relay 29, and the activation of alarm 30.

In particular, whereas a measurement of reaction torque by a mechanical means has been described in detail, any method of measuring the power required to create the alternating pressure variations could be employed with equally successful results. These could include the measurement of the electrical power required to drive the mechanism as well as various other mechanical, hydraulic or electrical means of measuring the torque of the driving motor. The function central to the successful operation of the detection means is the measurement of the power required to drive the While I have thus described herein a specific method and apparatus in a schematic form, it would be obvious to those skilled in the art that many individual variations may be made therein without departing form the spirit or scope of the invention.

I claim:

.1. An infrasonic intrusion detector for use in a confined space comprising a. means for generating alternating infrasonic over and under pressure variations within a confined space, said pressure alternating with respect to ambient exterior pressure.

b. means responsive to the atmpospheric resistance encountered by said generating means as said generating means generates pressure variations within said protected volume,

c. detector means for detecting any change in the atmospheric resistance encountered by said responsive means,

d. alarm means activated by said detecting means to.

provide an alarm signal upon a change in said resistance.

2. An infrasonic intrusion detector as claimed in claim 1 wherein said pressure generating means comprises a movable baffle positioned within a wall which defines said confined space.

3. An infrasonic intrusion detector as claimed in claim 2 wherein said space is a dwelling and said wall is a ceiling.

4. An infrasonic intrusion detector as claimed in claim 1 wherein said means for generating alternating pressure variations alternated at a rate less than 10 cycles per second.

5. An infransonic intrusion detector as claimed in claim 2 wherein said detector means comprise a resilient means mounted adjacent said baffle and connected to a dashpot which restrains said resilient means through a predetermined amplitude of excursion.

6. An infrasonic intrusion detector for use in protecting a confined space comprising a. movable baffle means mounted in a perimeter wall defining said confined space, said baffle generating alternating pressure variations within said space,

b. motor means for moving said baffle, said motor means mounted on a reaction means which includes a resilient reaction element between said motor means and said perimeter wall,

c. resilient contact means mounted on said reaction means, said contact means mounted adjacent a fixed contact means, said resilient contact being restrainedby a dashpot means from engaging said fixed contact means during normal excursions of said baffle means, said resilient contact engaging said fixed contact when the amplitude of motion of said reaction element exceeds a predetermined distance,

d. alarm signal means activated by the closing of said contacts to provide an alarm signal when said amplitude of motion exceeds a predetermined distance.

7. An infrasonic intrusion detector as claimed in claim 6 wherein said space is a dwelling and said wall is a ceiling.

8. An infrasonic intrusion detector as claimed in claim 6 wherein said baffle means generates alternating pressure variations at a rate less than 10 cycles per second.

9. An infrasonic intrusion detector for use in a confined space comprising,

a. means of generating alternating infrasonic over and under pressure variations within a confined space, said pressure alternating with respect to ambient exterior pressure,

b. means for monitoring the power required to create the pressure differential encountered by said alternating pressure generating means,

c. detecting means for detecting any change in the average power required to drive said alternating pressure means and,

d. alarm means actuated by said detecting means to provide an alarm signal upon a change in said power level.

10. An infrasonic intrusion detector as claimed in claim 9 wherein said means for generating alternating pressure variations comprises a movable baffle, and said detecting means comprises a resilient means mounted on said baffle and connected to a dashpot which restrains said resilient means through a predetermined amplitude of excursion. 

1. An infrasonic intrusion detector for use in a confined space comprising a. means for generating alternating infrasonic over and under pressure variations within a confined space, said pressure alternating with respect to ambient exterior pressure, b. means responsive to the atmpospheric resistance encountered by said generating means as said generating means generates pressure variations within said protected volume, c. detector means for detecting any change in the atmospheric resistance encountered by said responsive means, d. alarm means activated by said detecting means to provide an alarm signal upon a change in said resistance.
 2. An infrasonic intrusion detector as claimed in claim 1 wherein said pressure generating means comprises a movable baffle positioned within a wall which defines said confined space.
 3. An infrasonic intrusion detector as claimed in claim 2 wherein said space is a dwelling and said wall is a ceiling.
 4. An infrasonic intrusion detector as claimed in claim 1 wherein said means for generating alternating pressure variations alternated at a rate less than 10 cycles per second.
 5. An infransonic intrusion detector as claimed in claim 2 wherein said detector means comprise a resilient means mounted adjacent said baffle and connected to a dashpot which restrains said resilient means through a predetermined amplitude of excursion.
 6. An infrasonic intrusion detector for use in protecting a confined space comprising a. movable baffle means mounted in a perimeter wall defining said confined space, said baffle generating alternating pressure variations within said space, b. motor means for moving said baffle, said motor means mounted on a reaction means which includes a resilient reaction element between said motor means and said perimeter wall, c. resilient contact means mounted on said reaction means, said contact means mounted adjacent a fixed contact means, said resilient contact being restrained by a dashpot means from engaging said fixed contact means during normal excursions of said baffle means, said resilient contact engaging said fixed contact when the amplitude of motion of said reaction element exceeds a predetermined distance, d. alarm signal means activated by the closing of said contacts to provide an alarm signal when said amplitude of motion exceeds a predetermined distance.
 7. An infrasonic intrusion detector as claimed in claim 6 wherein said space is a dwelling and said wall is a ceiling.
 8. An infrasonic intrusion detector as claimed in claim 6 wherein said baffle means generates alternating pressure variations at a rate less than 10 cycles per second.
 9. An infrasonic intrusion detector for use in a confined space comprising, a. means of generating alternating infrasonic over and under pressure variations within a confined space, said pressure alternating with respect to ambient exterior pressure, b. means for monitoring the power required to create the pressure differential encountered by said alternating pressure generating means, c. detecting means for detecting any change in the average power required to drive said alternating pressure means and, d. alarm means actuated by said detecting means to provide an alarm signal upon a change in said power level.
 10. An infrasonic intrusion detector as claimed in claim 9 wherein said means for generating alternating pressure variations comprises a movable baffle, and said detecting means comprises a resilient means mounted on said baffle and connected to a dashpot which restrains said resilient means through a predetermined amplitude of excursion. 